M4A Versus MP3

Not so long ago, MP3 was the clear choice for compressed audio files but now, there's a new kid on the block: M4A. Here's how this format, made popular by Apple in applications such as iTunes, stacks up against the venerable MP3.

M4A

M4A, short for MPEG 4 Audio, refers to a compressed audio file in the MPEG-4 container format. Although the only official filename extension defined by the MPEG-4 standard is .mp4, MPEG-4 files that only contain audio typically have a file extension of ".m4a". The .mp4 extension is used for MPEG-4 files containing both audio and video. Songs that include copyright protection have an .m4p extension.

Apple Inc. popularized the .m4a filename extension, which is used in iTunes for songs encoded using either the lossy Advanced Audio Coding (AAC) or the Apple Lossless (ALE, ALAC) codec. M4A audio files with Apple Lossless compression are generally about half the size of the original file whereas those with AAC lossy compression can be as small as 1/10 the size of the original file. Note that AAC was designed to be the successor to MP3.

MP3

MP3, short for MPEG-1 Audio Layer III, is a digital audio codec or method for compressing and decompressing digitized audio. MP3 was designed by the Moving Picture Experts Group (MPEG) as part of its MPEG-1 standard. The initial group consisted of several teams of engineers at the Fraunhofer Institute, University of Hannover, AT&T-Bell Labs, Thomson-Brandt, CCETT, and others. The initial release of the MP3 format occurred in 1992 but it didn't really catch on until several years later when music sharing on the Internet became widespread.

MP3 employs a lossy compression technique known as perceptual coding or perceptual noise shaping that selectively eliminates sounds that are considered to be beyond the auditory resolution of most people. M4A AAC compression has similar objectives but it delivers a number of other improvements such as higher efficiency, better handling of certain audio frequencies, and greater flexibility for developers. For both formats, the size and sound quality is directly related to the sampling or bit rate which generally ranges from 96 to 320 kilobytes per second (Kbps). As the bit rate increases, the sound quality increases but so does the file size.

A number of utilities exist to convert M4A ACC audio to MP3. In fact, iTunes can even be used for this purpose (although it will not convert DRM protected audio).

Industry Support

MP3 has been the de facto standard for digital music files since the 1990's. Almost every computer media player recognizes and plays MP3 files, making them very popular for downloading and exchanging music with others. Although MP3 is somewhat dated compared to M4A, it has proven to be surprisingly resilient and is not likely to go away anytime soon.

However, industry support for M4A and MPEG-4 in general has been growing. Most audio/video players capable of playing MPEG-4 files will recognize M4A audio files. AAC is the default audio format for numerous products/services including the iPad, iPhone, iPod, iTunes, Nintendo DSi, DivX Plus Web Player and PlayStation 3. In short, M4A is catching up.

Sound Quality

For obvious reasons, an M4A audio with Apple Lossless compression delivers the best sound quality since none of the original signal is lost. For M4A audio encoded with AAC lossy compression, blind tests indicate that it provides greater sound quality and transparency than MP3 files coded at the same bit rate, particularly for bit rates at or below 128 Kbps. However, as bit rate increases and more of the original sound signal is preserved, the relative advantage of AAC over MP3 becomes less obvious.